[boost] [spirit] 'nother patch, (building example5.cpp on gcc4.2), attribute_transform.hpp

From: troy d. straszheim (troy_at_[hidden])
Date: 2008-05-29 17:07:06

Hi again guys,

This one is easier.
Having applied the assign_to/construct patch, examples 4 and 6 compile fine,
but example5.cpp died on this:

example5.cpp:283:   instantiated from here
../boost/trunk/boost/spirit/home/support/attribute_transform.hpp:144: error:
     ambiguous class template instantiation for 'boost::spirit::traits
     ::strip_single_element_sequence<
         boost::fusion::vector<
             boost::variant<
                 unsigned int, string, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_
             >, boost::fusion::void_, boost::fusion::void_
           , boost::fusion::void_, boost::fusion::void_, boost::fusion::void_
           , boost::fusion::void_, boost::fusion::void_, boost::fusion::void_
           , boost::fusion::void_
         >, mpl_::bool_<false>
     >'
../boost/trunk/boost/spirit/home/support/attribute_transform.hpp:144: error:
     invalid use of incomplete type 'boost::spirit::traits
     ::strip_single_element_sequence<
         boost::fusion::vector<
             boost::variant<
                 unsigned int, string, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_
             >, boost::fusion::void_, boost::fusion::void_
           , boost::fusion::void_, boost::fusion::void_, boost::fusion::void_
           , boost::fusion::void_, boost::fusion::void_, boost::fusion::void_
           , boost::fusion::void_
         >, mpl_::bool_<false>
     >'
../boost/trunk/boost/spirit/home/support/attribute_transform.hpp:32: error:
     declaration of 'boost::spirit::traits::strip_single_element_sequence<
         boost::fusion::vector<
             boost::variant<
                 unsigned int, string, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_, boost::detail::variant::void_
               , boost::detail::variant::void_
             >, boost::fusion::void_, boost::fusion::void_
           , boost::fusion::void_, boost::fusion::void_, boost::fusion::void_
           , boost::fusion::void_, boost::fusion::void_, boost::fusion::void_
           , boost::fusion::void_
         >, mpl_::bool_<false>
     >'

You just disambiguate via enable_if to get things building.  Works on gcc4.2:

--- attribute_transform.hpp	(revision 45915)
+++ attribute_transform.hpp	(working copy)
@@ -11,6 +11,7 @@
  #include <boost/spirit/home/support/unused.hpp>
  #include <boost/spirit/home/support/component.hpp>
  #include <boost/spirit/home/support/attribute_of.hpp>
+#include <boost/spirit/home/support/detail/values.hpp>
  #include <boost/fusion/include/vector.hpp>
  #include <boost/fusion/include/is_sequence.hpp>
  #include <boost/variant/variant_fwd.hpp>
@@ -25,16 +26,19 @@

      namespace traits
      {
+      using boost::spirit::detail::not_is_variant;
+
          // Here, we provide policies for stripping single element fusion
          // sequences. Add more specializations as needed.
-        template <typename T, typename IsSequence>
+      template <typename T, typename IsSequence, typename Enable = void>
          struct strip_single_element_sequence
          {
              typedef T type;
          };

          template <typename T>
-        struct strip_single_element_sequence<fusion::vector<T>, mpl::false_>
+        struct strip_single_element_sequence<fusion::vector<T>, mpl::false_,
+					     typename boost::enable_if<not_is_variant<T> >::type>
          {
              //  Strips single element fusion vectors into its 'naked'
              //  form: vector<T> --> T
@@ -42,7 +46,8 @@
          };

          template <typename T>
-        struct strip_single_element_sequence<fusion::vector<T>, mpl::true_>
+        struct strip_single_element_sequence<fusion::vector<T>, mpl::true_,
+					     typename boost::enable_if<not_is_variant<T> >::type>
          {
              //  Strips single element fusion vectors into its 'naked'
              //  form: vector<T> --> T, but does so only if T is not a fusion

Let me know if you just want a commit, (also for the other stuff).
There are a few more things like this around, I'll get after them.  Thanks for a great
library (these little gotchas notwithstanding).    I'm getting a
real kick out of all this, learning a lot...  this code is *crazy*.
You guys have definitely raised the bar.

-t